On my consumer unit I have 3 separate switches for sockets wihtin my house - suggesting that they are on 3 individual loops.
Am I correct in thinking that powerline adapters will only work if they are on the same loop?
They work better on the same loop. They start to loose speed when you go across fuse's and such things. You can even get them to work past the meter sometimes.
However they can also stop if you turn the washing machine on
Use a drilling machine / vacum cleaner. Stuff with electric motors normally causes the noise to kill the signal. Something that can help with a problem device is to install a really long extension on it (eg a vacum cleaner). Just like long adsl lines. It can kill the signal (in this case interference)
Or the worst I have seen a cheap ebay replacement laptop power supply. I could either charge the battery or use the net connection!!!